Regulatory Effects of Three Rhizosphere Growth-promoting Bacterial Agents on Nutrient Utilization, Yield, and Quality of Flue-cured Tobacco

Purpose The aim of this study was to investigate the effects of different microbial agents on soil nutrient activation and the growth and development of flue-cured tobacco in the Kunming tobacco-growing area, providing a theoretical basis for green and efficient tobacco production.

Methods A field experiment was conducted from April to September 2023 in Shilin Yi Autonomous County, Kunming City. Using no microbial agent application as the control (CK), the effects of three microbial agents, Stenotrophomonas sp. (T₁), Microbacterium sp. (T₂), and Herbaspirillum sp. (T₃) on agronomic traits, soil nutrients, plant nutrient status, dry matter accumulation, yield, and quality of flue-cured tobacco were investigated.

Results Compared with CK, the flue-cured tobacco leaf length and root dry weight (at 60 d), as well as plant height, stem dry weight, and leaf dry weight (at 90 d), were significantly increased in the microbial agent treatments. The proportions of medium and superior grade tobacco leaves were significantly increased in the T₁, T₂, and T₃ treatments; yield and output value were significantly increased in the T₂ treatment; and the average price was significantly increased in the T₃ treatment. Overall, the T₂ treatment performed best. In terms of soil properties, available phosphorus (at 60 and 90 d) and organic matter contents (at 60 d) were significantly increased in all treatments. Additionally, total phosphorus (at 60 and 90 d), ammonium nitrogen (at 90 d), available potassium (at 60 d), and total potassium contents (at 60 d) were significantly increased in the T₂ treatment. Regarding nutrient accumulation, the T₂ treatment increased the allocation of nitrogen and potassium in tobacco stems, reduced nitrogen allocation in roots, and significantly enhancing the total yield and economic value of flue-cured tobacco; the T₃ treatment increased the uptake and allocation of phosphorus and potassium in tobacco roots, appropriately reduced nitrogen accumulation at the later growth stage, effectively improved the appearance characteristics of tobacco leaves, and simultaneously increased the proportion of high-quality leaves.

Conclusion The three microbial agents used in this study demonstrated significant effects in improving soil nutrient content, regulating nutrient accumulation in flue-cured tobacco, and enhancing tobacco leaf yield and output value, with the Microbacterium sp. treatment showing the best effect. The results provide a theoretical basis for the rational application of microbial agents in flue-cured tobacco production in the Kunming tobacco-growing area.